I've used a router table as a jointer but in a bit different way. I'll set a 1/2" or 3/4" straight cutter about 1/32" narrower than the width of the board then run the board through, against the rotation of the blade. This only works for small boards that are shorter than the length of the router table fence and use a feather board as one slipup and you'll have a wavy edge. Do this to both edges, readjusting the fence another 1/32" for the 2nd edge.
As far a tongue and groove, as many have said, it's not really necessary with good flat edges and enough clamps BUT if you just want to do it for looks, just use the table saw as someone mentioned. 1/8" kerf would be ideal but not essential. Just cut the groove in one board, running the board through once then flipping around and running through again. This makes a groove that's perfectly centered. It's not necessary other than aesthetics. Attach a sacrificial board to the fence, adjust over to the blade then cut the tongue on the other workpiece, adjusting as necessary until the tongue fits snugly. No as complicated as all that sounds and a fairly quick method. Good luck